The utilization of wave motion or other erratic motion as a power source has long been recognized and any number of suggestions have been put forward as to how the energy might but put to practical use. One of the earlier concepts along these lines is illustrated in the Hansen patent 1,799,848 where a wave motor is disclosed in the form of a floating barge with pistons connected between it and the bottom. The main difficulty in the operation of this type of device is the fact that wave motion is not uniform and it will not produce uniform pressure outputs with standard piston compressors. Therefore, it is advantageous to utilize a novel design of a compressor where in effect the head of the compressor may be varied in distance from the main pumping piston so that uniform output pressures can be achieved in spite of the fact that varying strokes may be encountered.